Biogenic amine O- and N-methyltransferase will be purified from mammalian tissues and further characterized to define their properties. The specific enzymes are catechol-O-methyltransferase (COMT), phenethanolamine-N-methyltransferase (PNMT), indoleamine-N-methyltransferase (INMT), hydroxyindole-O-methyltransferase (HIOMT), and histamine-N-methyltransferase (HNMT). Among these enzymes, COMT has been shown by us to exist in mammalian tissues including those of human as two distinct molecular forms, designated COMT I and COMT II, which differ from each other in their molecular size and charge. Although our extensive physical and kinetic studies on the two variant forms of COMT are consistent with the hypothesis that the two forms are genetically dissimilar proteins, the exact nature of the muliplicity of COMT is not known, nor is its physiological function. The proposed work will involve further characterization of COMT I and COMT II with a special emphasis on elucidation of the molecular basis of the enzyme multiplicity and determination of the relationship between structure and enzyme activity. Attempts will be made to isolate the two physical forms of COMT in homogeneous form by a procedure involving affinity chromatography combined with conventional purification techniques, after which extensive chemical studies will be carried out. In addition to COMT, other biogenic amine methyltransferases will also be further studied to define their properties - tissue distribution, pH optimum, cofactor requirement, substrate specificity, molecular, physicochemical, catalytic, and kinetic properties.